1. Field of the Invention
This invention relates to the chemical treatment of cellulosic materials. More particularly, the invention relates to the treatment of wood and its derivative materials to obtain increased resistance to rot while improving dimensional stability.
2. Description of the Prior Art
Although wood possesses many unique and desirable properties, serious problems have resulted from the fact that cellulosic materials retain water in the fiber molecules; in the fine capillary structure within the fiber wall; and mechanically in the coarse capillary structure between the fibers and within the cell lumen or fiber cavity. Decay organisms proliferate in this environment and often cause rapid deterioration of the cellulosic material. It has been found that by changing the hydrophilic nature of wood through chemical modification the substrate or wood cellulose is rendered unrecognizable as a food source to support microbial growth. In drying the substrate below the fiber-saturation point, however, the bound water held intimately between the fine structural units, of which cellulosic materials are composed, is removed and these structural units are drawn closer together to occupy or eliminate the void area produced by the removal of this water. Upon return of this moisture to the cell walls the wood swells and returns to its original state.
In developing a treatment which will render the cellulosic material resistant to rot while at the same time maintaining or even increasing its dimensional stability, several criteria must be met. In whole wood, accessibility of the treating reagent to the reactive chemical sites is a major consideration. It is advantageous, therefore, that the reagents used for the chemical modification of wood be volatile for good penetration and for ease of removal after reaction. The reagent should react quickly with the wood component hydroxyl groups at low temperatures under mild conditions. There should be 100 percent carbon skeleton add-on of chemical so that no byproducts need be removed. The chemical bonds formed should be stable to ensure permanence. For dry wood, a solvent (which may be the reagent itself), preferably will be used to swell the wood structure and thus facilitate penetration of the cell wall by the reagent. The treated wood should still possess the desirable properties of untreated wood, with the only properties modified being decay resistance and dimensional stability.
Although several methods of chemically treating wood designed for stabilizing the dimensions of wood and other cellulosic materials have been suggested, most have failed in achieving any real commercial significance. In general, the prior art methods suffer from one or more of the following disadvantages: the process is too cumbersome or time consuming; the process is excessively expensive; the process is substantially ineffective under a wide range of exposure or the treatment imports undesirable properties to the product.
It is previously known (U.S. Pat. No. 3,183,114) that by impregnating wood with either ethylene oxide or propylene oxide, that the rot resistance of cellulosic materials may be increased while also increasing the anti-shrink efficiency. The present invention is a process which allows much less expensive treatment than is characteristic of ethylene oxide treatment and is considerably more effective than using propylene oxide. Ethylene oxide has a boiling point of 10.degree. C. so is in a gaseous state at atmospheric pressure. This treatment therefore necessitates the use of cumbersome and expensive pressure vessels, piping and auxiliaries. Butylene oxide, with a boiling point of 63.degree. C., is a liquid at room temperature and pressure and so requires none of this equipment. It may be used to treat a cellulosic sample either in this state or in a gaseous form at elevated temperatures.
Propylene oxide has a boiling point of 35.degree. C. and is therefore a liquid at room conditions. It has been found, however, that a butylene oxide treatment is superior to that using propylene oxide in both anti-shrink efficiency and rot resistance. Tables 1 and 2 show the superior ASE and superior rot resistance can be illustrated by the following example: samples soaked to a weight percent add-on of 7 percent butylene oxide were innoculated with the fungus Lenzites trabea and later weighed to determine the weight loss due to deterioration. After 6 weeks the loss was 5.2 percent and after 12 weeks 18.8 percent. When treated with as much as 50 percent weight add-on propylene oxide, the loss was still greater than that treated with 7 percent butylene oxide (6.5 and 25.2 percent respectively).
The present invention is believed to have several advantages over the prior art in treating wood or its derivative material:
1. Eliminates the need for expensive sealed containers, piping and auxiliaries which are necessary with treating chemicals which are normally in a gaseous form. PA1 2. Allows for treatment either in a liquid or a gas phase without excessive temperatures or pressures. PA1 3. The process offers considerably greater range of chemical modification at lower treatment concentrations.